1. Field of the Invention
The present invention relates to droplet discharge heads, for example inkjet heads or the like, droplet discharge apparatuses, and image forming apparatuses provided therewith. More particularly, the present invention relates to droplet discharge heads provided with a memory for storing data.
2. Description of the Related Art
A droplet discharge head and a droplet discharge apparatus provided therewith are described below by using an inkjet print head and an inkjet printer provided therewith. In the inkjet print head, nozzle variation occurs in the same head as well as among the heads. Accordingly, to perform printing uniformly and at high precision, it is necessary to reduce the nozzle variation. This can be achieved by individually setting a profile, such as a driving waveform, for each head.
However, a heavy-duty and speedy inkjet printer, which performs volumes of printing at high speed, has many inkjet print heads. For example, such printers may have several hundred heads. With such a vast number of heads, it is impractical to manually set the profile for each head. To solve this problem, in some printers a nonvolatile memory is mounted on each head. A profile, such as setting information on the driving waveform that agrees with each of the heads, is written in the nonvolatile memory in advance, and when the head is mounted on the printer, the profile is read from the nonvolatile memory. As a result, a driving condition, such as the driving waveform that agrees with the head, is automatically set for each head by the printer. A related technology has been disclose in, for example, Japanese Patent Application Laid-open No. H7-171955 and Japanese Patent Application Laid-open No. 2003-237045.
Damage to the contents stored in the nonvolatile memory, such as basic information on the head, e.g., the profile such as the setting information on the driving waveform or a head individual number, needs to be avoided. From this view point, read-only PROMs or EPROMs are preferably used as the nonvolatile memory.
By aiming at controlling a characteristic change in the head or service life of the head, there is a strong demand for storing the number of times a pressure generating element is driven, the number of times a surface of a nozzle is cleaned by a wiper, operation hours, or the like (for example, Japanese Patent Application No. H5-108380 and Japanese Patent Application Laid-open No. H8-281927). To meet these demands, when a rewritable EEPROM or flash memory is used as a nonvolatile memory, the risk of damage due to an unexpected incident affecting the basic information about the head, which should not be deleted, is higher compared with a case where a read-only nonvolatile memory is used. Such unexpected incidents include a specification error in an address for writing data, a handling error, an extreme low-voltage state when turning a power supply on or off, a control error, noise, or the like.
To cope with such a problem, conventionally, a read-only ROM and a rewritable RAM are separately mounted. Basic information that should not be deleted is written in the ROM, and information that needs to be rewritten is written in the RAM (for example, Japanese Patent Application Laid-open No. H6-40086).
In recent years, as the density of the nozzles on inkjet heads has increased, an inkjet head with a structure in which a plurality of nozzle rows with the same structure are arranged to form a single head has become popular. A head in which each of the nozzle rows with the same structure includes a circuit board mounted with a nozzle selecting element is widely used. Similar to the conventional technology, it is conceivable that both a read-only nonvolatile memory and a rewritable nonvolatile memory are mounted on the same board; however, costs increase if the read-only nonvolatile memories and the rewritable nonvolatile memories are each mounted on all of the boards.
It is also conceivable that two types of board are used: a board mounted with both the read-only nonvolatile memory and the rewritable nonvolatile memory and a board without mounting the nonvolatile memory even though the same type of board is used. However, the unit price of parts cannot be reduced due to a decrease in order quantity of the boards, and, moreover, the stock control is complicated. It is also conceivable that, instead of mounting a nonvolatile memory on the same board equipped with the nozzle row with the same structure, the boards with the same structure equipped with the nozzle rows with the same structure are connected to another second board all together, on which both the read-only nonvolatile memory and the rewritable nonvolatile memory are mounted. In such a case, two types of board also need to be prepared; therefore, the cost is increased and stock control becomes complicated.
Among EEPROMs, there is a type of, for example, 25LC040 manufactured by Microchip Technology, Inc., having a read-only address space and a rewritable address space in a single device; however, in such a device, the write-protected area is small and the device is not I2C bus type, which causes a problem in that the choice of EEPROM is limited.
A method of arranging a controller and setting a read-only memory block and a rewritable memory block has been proposed in, for example, Japanese Patent Application Laid-open No. 2004-164632, Japanese Patent Application Laid-open No. 2005-108273, and Japanese Patent Application Laid-open No. S62-278650. With this method, although it is possible to cope with a specification error in an address for writing data or a handling error, there sometimes is a case of not being able to cope with damage to data due to noise or the like, and, moreover, design is complicated because a controller for the memories needs to be arranged.
A method in which a controller and a plurality of types of memories are arranged and non-rewritable data and data to be rewritten are determined for storage therein is proposed (for example, Japanese Patent Application Laid-open No. S62-162141); however, because it is necessary to install a controller for the memories, the design is also complicated.
A method of, when data is written, disconnecting a wiring line of a memory, which stores data to be protected, with a switch is proposed (for example, Japanese Patent Application Laid-open No. 2007-164622). With this method, the cost of providing the switch is required, and moreover, the design is complicated because a controller for the switch needs to be arranged.